A space frame is a three-dimensional structure built on struts locked together. These structures can accommodate very heavy weight with limited materials and supports.

Open lattice towers were used for early utility-scale wind turbines with unfortunate results. Bolts were rattled loose, leading to structural failures, and birds took up perches, leading to serious avian mortality.

In searching for a way to cut costs, GE engineers returned to the lattice. But the space frame eliminates danger to avian life by enclosing the lattice with a translucent, non-weight-bearing, UV-protected PVC-polyester fabric coating.

“The direction of the wind industry is higher hub heights,” Longtin said. “But tube towers scale poorly because increasing load and material requirements do not pay off in increased output.”

GE’s R&D goal is to scale towers up and keep costs down. The space frame’s ten-meter diameter base will allow a 120-meter tower to use 20 percent to 30 percent less steel than a traditional 100-meter tube tower because the broader base means less support is needed from the tower walls.

Because the space frame narrows at its top, it can interface with any nacelle without structural alterations.

One of the two key design parameters of the space frame, Longtin said, was limiting all parts to the 40 foot size of a standard shipping container so all the pieces of a tower can be delivered by long haul trailers. That should have a significant impact on transportation logistics.

The space frame will arrive in shipping containers. On-site assembly will replace complex transport logistics. It took about 30 days to assemble the Tehachapi prototype, but Longtin believes the average assembly time can be four days.

The other key design parameter was that the fastening system be maintenance free. The space frame’s splined bolts, once inserted, are essentially like rivets. They have long been the standard, maintenance-free fasteners used in bridges, aircraft carriers, and skyscrapers. Accelerated testing by GE engineers and third party labs validated the maintenance-free durability of the GE splined bolts.

The cost savings from the space frame will be site specific, Longtin explained. Savings from reductions in materials, shipping time and costs may be offset by increased on-site labor and time.

Because the space frame’s economic advantages will be greater for taller towers, Longtin expects the balance to come out strongly in GE’s favor in heavily forested places like Sweden, where the rotor needs to be above the treetops, and in places like Northern Germany and the U.S. Southeast, where economic wind speeds are higher up.

An alternate strategy for cutting costs is substituting concrete for steel at the tower’s base. That can be cost effective if a project is near a concrete source, Longtin acknowledged. But many are not.

Siemens, one of GE’s biggest competitors, introduced a bolted steel design aimed at reduced costs for towers as tall as 140 meters in 2011. It offered many of the space frame’s advances. Bent steel plate shells and other parts can be delivered to the project site by standard trucking for on-site assembly with maintenance-free bolts. A broader base provides increased stability.

The concept, developed with Denmark’s Andresen Towers, has apparently failed to penetrate the marketplace. Requests for information from Siemens about the bolted steel design’s commercialization were unanswered. Queries to wind industry professionals turned up no awareness of the Siemens design. Like the space frame, success for the Siemens concept probably awaits greater demand for taller towers.

GE is presently working with ARPA-E on a truss-structured, fabric-covered turbine blade that can be shipped in containers and economically assembled onsite -- even as they continue to get bigger. These advances show that even in a maturing industry like wind, there are still plenty of logistics and costs to attack.

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So the fabric should resist: - big birds flying with an hard wind, so speeds of 100miles/hr (speed wind + speed bird) or so; - all types of chemicals around; - not become weaker over time; - neither stretch out over time (decades); etc.

I agree that this is a nice solution. Back to the future? Combines technology from the Wright Brothers (fabric over frame) with structural ideas from Alexander Graham Bell and Buckminster Fuller:

Space frames were independently developed by Alexander Graham Bell around 1900 and Buckminster Fuller in the 1950s. Bell's interest was primarily in using them to make rigid frames for nautical and aeronautical engineering, with the tetrahedral truss being one of his inventions. However few of his designs were realised. Buckminster Fuller's focus was architectural structures; his work had greater influence.*

Interesting article, the positive is eased transport also possibly greater local employment, and lower cost. The negative must be the visual impact and ugliness of the large area of covered lattice structure. A slim tower is a more elegant solution.

From a technical standpoint, the interesting development here is the fabric used to cover the framework. If it's able to resist sun and weather for up to 10 years before needing replacement, this could be a very positive development. Certainly it reduces the "embedded energy" content of the tower itself, and enables taller towers. Eliminating the need for escorted super wide-load transport of pre-fabricated tower sections is a big deal.

It's the opposite to the other direction one might go to reduce the amortized cost of towers for wind turbines. This approach seeks to reduce initial costs and allow capital invested in the tower to be recovered over a shorter time period. The alternative would be to build towers that would last for centuries. Support systems that would enable the turbines atop the towers to be repaired or replaced on a much shorter time scale would be needed. However, we'd have 20 years to develop them.

The problem with that alternative is that we're just not oriented, as a society, to think in terms of very long-term investments. For the way we operate, the lower-cost covered space frame approach makes more sense.

I have often wondered why we don't place the generator on the ground instead of up on the tower.

Wouldn't it be more cost effective if it were sitting on the ground and somethnig like hydraulics were used as the energy transfer mechanism to the ground? Or even something simple like a rotating shaft since the rotational speeds are low anyway. The gear box increasing generator rotational speed could also be on the ground.

Indeed! My generator, tranny, etc. are all on the ground with only my lightweight rotor in the air. My footprint is minimal and noise near nil. Look at Revolutions Wind and you'll see the wisdom of scalable distributed generation in a 5mph device at 10% of GE's cost.

Thomas,Energy losses and vulnerability (more maintenance sensitive) of your proposal will be higher. Probably the total investment costs too, but that I do not know for sure.

A vertical, rotating axe that brings 8MW down over a distance of 120m requires bearings in between, which imply more stability of the tower and more losses. Furthermore, I assume that a 90 degree gearwheel transmission has inherently more friction losses than a straight one.

As you suggest it might be difficult to allign and maintain a rotating mass of that length. Of course my first choice would be something that didn't involve either of these problems like some type of pumped fluid using flexible couplings at the top and bottom of the tower.

I too would be very interested in any studies have been done that have analyzed locating only a hydraulic pump that is connected to the wind turbine’s drive shaft at the top and then locating the hydraulic driven transmission/generator inside the structure on the ground, verses the traditional design where everything is located at the top, high above the ground.

I believe that since that there would be much less weight at the top (to be supported), then I believe that a much larger wind turbine could be supported by the towers that are already in production, which would be a win-win for US.

Note: The hydraulic fluid required could even flow through part of the structure itself, much like what is done in racing cars where parts of the chassis are used to carry similar fluids. A "holding/storage" tank at the bottom could hold all the required hydraulic fluids and should a leak develop, a valve at the top could quickly “empty” the lines into the holding/storage tank via gravity. Another potential benefit could be that the fluid itself could be used to cool all the components, which might increase their life span. Plus, If the transmission and/or generator needed to be serviced, having them located on the ground would be a major plus as compared to having them located inside a tight nacelle hundreds of feet above the ground!

Just do the calculations and compare with e.g. the 7.5MW direct drive Enercon wind turbine (no gearbox).Direct drive implies no friction except the bearings of the main spindle in the nacelle wich an hydraulic design also needs.

I have not seen an 8MW hydraulic pump without substantial friction losses, neither a motor without those losses, neither an 2x120meter long tube (to transport the fluid) without friction losses. But I'm not up-to-date regarding hydraulics.

Or better. After all one is like an organ pipe and has relatively non-disspiative walls so that under some circumstances resonance could be set up with relatively high Q. The other appears to be a relatively highly dissipative oddly shaped column that I would expect to have low Q and therefore little sound.